In reciprocating compressors an eccentric of a crankshaft is received in a bearing located at one end of the connecting rod. The eccentric rotates within the bearing as the crankshaft rotates and the bearing orbits with respect to the axis of the crankshaft. The other end of the connecting rod is connected to a piston through a wrist pin. Although one end of the connecting rod is undergoing an orbiting motion, the other end is held to a pivoting and reciprocating motion since the piston can only reciprocate. The crankcase pressure always acts on one side of the piston and this pressure is normally suction pressure. The other side of the piston is acted on by a range of pressures which ranges from less than suction pressure for unstaged compressors, or less than intermediate pressure for staged compressors, in order to draw gas into the cylinders, to greater than discharge pressure to overcome the system pressure and valve bias acting to hold the discharge valve closed.
Where less than suction pressure is acting on one side of the piston during the suction stroke, there is a pressure/load reversal across the piston during each cycle. Where intermediate pressure is being drawn into the cylinder, however, the differential pressure across the piston is always in the same direction and there is no pressure/load reversal.
Conventional journal bearings develop extremely thin lubricant films and consequently high friction and wear under duty cycles which combine nonreversing loading with limited journal angular oscillation. Where the bearing load reverses, a thick-film hydrodynamic lubrication condition is maintained as the journal is squeezed back and forth within the sleeve, but where the load never reverses, thin-film "mixed" lubrication conditions develop as the journal is gradually squeezed against the sleeve. One approach to the problem is to modify the bearing surface(s) in such a way that journal oscillation, however limited, can be used to develop thick-film hydrodynamic lubrication. Load sharing between segments of a composite bearing having offset centerlines varies dynamically with rotation and translation of the journal in the sleeve. Thus, as the journal "rocks" back and forth, the load carried by each segment is relieved periodically even if the total load is not.
Where composite bearings having offset centerlines have been employed, it has been necessary to split the bearing for assembly. Accordingly, the use of multiple offset segments have been limited to relatively large journal bearing wrist pin designs to produce squeeze film lubrication in nonreverse loading applications. The relatively small size of wrist pin bearings used for refrigeration compressors, and the like, do not permit the use of split bearings in assembly. A major reason that split bearings cannot be used in refrigerant compressors, or the like, is that a diametrical wrist pin clearance on the order of 0.0005 inches cannot be maintained, upon assembly, although it is necessary to achieve proper lubrication.